Light Management - Spectrum Technologies Field Scout CM1000 Operation Manual

Light Management

Natural sunlight is the best source of light for measuring
chlorophyll by reflectance because both wavelengths are
present in approximately equal quantities and the quantity
of light remains relatively constant. With artificial light
sources, the user must be aware that different light sources
emit light having different qualities. For example,
florescent lights emit more blue light and incandescent
lights emit more red light. The light sensors in the
CM1000 are sensitive enough to detect the cooling of the
filament in an incandescent light bulb as the 120 volt AC
current alternates from positive to negative and back again
at the rate of 60 Hz. The sensitivity of the meter to light
quality enables the meter to estimate the chlorophyll
content of leaves.
When using artificial light, the CM1000 senses light
quantities using a time period that takes into consideration
the 60 Hz alternating current used by electric power
companies in the U.S. The meter must be reconfigured to
be used in Europe and other regions where 50 Hz AC
power is used. Compared to light generated with AC
current, DC light sources provide a steady light output. In
some situations, it may be easier to use a DC light source
than to concern oneself with the frequency qualities of
AC.
It is important to develop a standard method for taking
readings with the CM1000. Ideally, the sun is always at
the user's back and the line between the sample and the
sensors is approximately parallel to the sun's rays. The
ambient light sensors are behind the white Teflon dots in
the black rectangular box on top of the yellow case.  The
Teflon dots diffuse the ambient light and protect the
ambient light sensors. The user can tilt the black box so
that the ambient light sensors are directly facing the sun,
thereby enhancing the capture of ambient light.
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